This invention relates generally to loss of voltage sensors, and in particular to circuitry for sensing the loss of voltage in a power distribution system.
It is often necessary in commercial electrical distribution systems that certain procedures be followed in the event of a power interruption. For example, some customers maintain their own electrical power generating equipment which must be started in the event of a power failure to maintain critical equipment in operation. Other customers automatically disconnect all electrical eqipment from the commercial power mains in the event of a power failure so that critical equipment can be reenergized in a deliberate and systematic manner after service is restored. Furthermore, in the case of multi-phase power systems, it is desirable to disconnect equipment following a failure in one supply phase in order to avoid potentially damaging single-phase operation. Voltage loss sensors, particularly those adapted for use with commercial power distribution systems, are useful for automatically implementing such procedures in the event of a power failure.
In the case of high voltage power mains, capacitive coupling of the loss of voltage sensor circuitry to the power mains is desirable in order to provide isolation from the high voltages present in the conductors. The loss of voltage sensor of the present invention utilizes such preferred capacitive coupling for both energization of its circuitry and for providing an alarm signal. With this sensor, coupling to the high voltage conductor of a power distribution system is readily accomplished at such conventional locations as underground cable termination test points, insulators, or by means of suitably insulated winding disposed within the electric field of the conductor.
Because the procedures to be followed in the event of a power failure vary from user to user and from situation to situation, the output response of a loss of voltage sensor should be suitable for actuating a variety of other cirucitry in the event of a power failure. Thus, a general type of electrical response, such as the closure of a set of relay contacts, is often a desirable output, since such a contact closure can easily be adapted to actuate other electrical systems and equipment.
Furthermore, since it is often desirable to monitor a number of different points in an electrical system, loss of voltage sensors may be used in great numbers. Consequently, it is desirable that such sensors be of relatively small physical size so as to facilitate placement within existing electrical systems. It is also desirable that such sensors be easily and economically manufactured so as to allow their wide spread use without excessive cost.
Accordingly, it is a general object of this invention to provide a new and improved loss of voltage sensor.
It is another object of this invention to provide a loss of voltage sensor suitable for use in conjunction with high voltage electrical power mains.
It is still another object of this invention to provide a new and improved loss of voltage sensor which may be energized and triggered by means of capacitive coupling to a high voltage power mains cable.
It is still another object of this invention to provide a new and improved loss of voltage sensor which may be easily and economically manufactured.